What is earth fault relay and how is it different from RCCB?

The earth fault relay is a type of relay that can sense the faults between the phase and earth. The major function of an earth fault relay is to operate for the leakage currents to the earth. This relay can detect the earth’s fault, so we can say that RCCB does the same function. The earth fault relay is an advanced device, RCCB is used to prevent electric shock and thus it can provide human protection but the EFR is not used for human protection it is used to protect the equipment.

The EFR deals with high voltage and high current related protection, earth fault relays are used in distribution panels, transformers, substations, etc. The major difference between an EFR and RCCB is the RCCB is a protection device, CT, tripping mechanism, etc. But the EFR is a sensing device its input is given by an external CT and it’s out will be given to any breaker such as contact breaker and then this device will do the tripping mechanism. So an EFR is a monitoring device that needs a CT to give the input and its output is given to a breaker.

How does an earth fault relay work?

So as we discussed above the EFR is an earth fault monitoring device and it needs a CT to give input. If the earth fault current remains above the setting for the set time delay then the output tripping contacts would operate. The EFR can be used for high amperes and its values can be set by using a dipswitch. We can set the parameters of the EFR like its tripping, current, tripping, time, high peak current, etc.

The working of an EFR is similar to an RCCB it works according to Kirchoff’s law, this law says that the current that goes to a point must be equal to the current that comes back from that point. But in case of an earth fault the current values will be very different and to determine this fault we use an EFR. So the fault can be detected by EFR, CT will help to determine the fault CT will be connected to an EFR so if the current that sent and received is same then there won’t be any induced EMF in CT if not then an EMF will be induced in CT and this output of the EMF will be sent to relay.

We can see certain parameters in EFR such as IS which is sensing current then IHS which is high sensing current and also we can see a delay so we can set all these values in an EFR with the help of a dipswitch. So when the EFR senses any fault then the trip light will be ON, after clearing the fault we need to reset the EFR. Certain models of EFR provide earth fault protection and overcurrent protection and sometimes EFR won’t have an inbuilt CT so we must connect a CT to the ERF separately.


post-graduate in Electronics & communication.

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